It’s a question researchers have been grappling with for a while, if a forthcoming paper in the Annual Review of Clinical Psychology is any indication. That paper, lead-authored by Joshua Miller, a personality researcher at the University of Georgia, offers a helpful summary of the current academic controversies surrounding narcissism, and perhaps the most important one has to do with the trait’s etiology — that is, what causes it. (The research isn’t online yet, but I’ll come back and add a link once it is.)

Before proceeding, it’s important to remember that narcissism can pop up in one of two ways: There’s vulnerable narcissism — think George Costanza, neurotically desperate for validation — or grandiose narcissism, in which the subject has an overblown view of themself and their abilities. The two types aren’t necessarily linked to the same factors.

As Miller and his colleagues explain, “theoretical speculation far outweighs empirical evidence” when it comes to narcissism. A great deal of attention has centered around parenting styles, and here there are two sets of theories which make effectively opposite claims. On the one hand are “psychodynamic theories that suggest cold, non-validating, or dismissive parenting may foster the development of [narcissistic] traits,” with those traits acting “as a façade hiding an underlying fragility” — that is, narcissists are compensating for the lack of love and attention they got from their parents. On the other hand are theories which suggest that narcissists’ parents showered them with too much attention, and that it went to their head: My parents said I’m the most important person in the world, so I must be!

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If you’re a researcher hoping to shine light on this subject, you’ll likely resort to one of two kinds of studies. Retrospective studies involve asking adult subjects to answer questions about their childhood. Such studies are fairly easy to conduct, since all you have to do is ask someone questions, but they’re susceptible to certain types of bias that can confound the results: Maybe people who are narcissistic are also more likely to remember their childhood in a certain way. Prospective studies, on the other hand, skirt this problem by gathering data about parenting styles at the time the subject is still a child, and then following up with them later on to see whether and to what extent they developed narcissistic tendencies as a result. The downside is time and expense: You need to find a group of kids, gather data, and then collect that follow-up data many years later.

Overall, Miller and his colleagues report, the data on parenting and narcissism is limited, but it appears that grandiose and vulnerable narcissism “are linked to different etiological factors[.]” Grandiose narcissism is linked to “slightly more permissive parenting or parental overvaluation (or with no associations to parenting at all) and vulnerable narcissism with colder, more controlling/intrusive, or inconsistent parenting.” If these links hold up, then there might be something to the idea that intuitively logical parenting that is too “warm” could lead a child to develop an inflated sense of self, and parenting that is too “cold” could lead the child to develop a lingering neediness.

But the researchers are careful here: “There is still a great deal of work to be done in this area … especially with the use of prospective designs,” they note. Those are the studies that really can tell us the most.

Parenting can only explain so much, anyway. Genes seem to be a pretty big part of the picture as well. One prospective study, Miller and his colleagues write, “found that preschoolers who were rated as being interpersonally antagonistic, impulsive, histrionic, high in activity, and attention seeking were generally rated as more narcissistic in adolescence and early adulthood, which may suggest that these traits arise quite early in life.” Other research found “a substantial genetic” connection to narcissism. As with so many other aspects of personality and life outcomes, what’s going on here is a complicated mix of nature and nurture.